Process for producing aliphatic oligocarbonate diols

ABSTRACT

The present invention relates to a process for producing an aliphatic oligocarbonate diol comprising a) reacting an aliphatic diol with dimethyl carbonate at an elevated pressure in a reaction mixture, and b) subsequently removing unreacted methanol and dimethyl carbonate under a reduced pressure to uncap the terminal OH groups.

FIELD OF THE INVENTION

[0001] The present invention relates to a new process for producingaliphatic oligocarbonate diols by the transesterification of aliphaticdiols with dimethyl carbonate (DMC) under elevated pressure. The processaccording to the invention also makes it possible to produce aliphaticoligocarbonate diols on a large industrial scale and with a highspace-time yield (STY) from readily available DMC.

BACKGROUND OF THE INVENTION

[0002] Aliphatic oligocarbonate diols are important precursors for theproduction of plastics, lacquers and adhesives, for example. They arereacted with isocyanates, epoxides, (cyclic) esters, acids or acidanhydrides, for example. They can be produced from aliphatic diols bythe reaction thereof with phosgene (e.g. DE-A 1 595 446), esters ofbis-chlorocarbonic acid (e.g. DE-A 0 857 948), diaryl carbonates (e.g.DE-A 1 915 908), cyclic carbonates (e.g. DE-A 2 523 352: ethylenecarbonate) or dialkyl carbonates (e.g. DE-A 2 555 805).

[0003] Of the carbonate sources, diphenyl carbonate (DPC), which is adiaryl carbonate, is particularly important, since aliphaticoligocarbonate diols of particularly high quality can be produced fromDPC (e.g. U.S. Pat. No. 3,544,524, EP-A 0 292 772). In contrast to allother carbonate sources, DPC reacts quantitatively with aliphatic OHfunctions, so that after removing the phenol which is formed, all theterminal OH groups of the oligocarbonate diol are available forreaction, e.g. with isocyanate groups. Moreover, only very lowconcentrations of a soluble catalyst are required, so that the lattercan remain in the product.

[0004] Processes based on DPC have the following disadvantages, however:

[0005] Only about 13% by weight of the DPC remains as CO groups in theoligocarbonate; the remainder is distilled off as phenol. Asignificantly higher proportion of dialkyl carbonates remains in theoligocarbonate, depending on the alkyl radical concerned. Thus about 31%by weight of dimethyl carbonate (DMC) is available as CO for theoligocarbonate, since the methanol which is distilled off has amolecular weight which is considerably lower than that of phenol.

[0006] Because high-boiling phenol (normal boiling point: 182° C.) hasto be separated from the reaction mixture, it is only diols with aboiling point considerably higher than 182° C. which can be used in thereaction, in order to prevent unwanted removal of the diol bydistillation.

[0007] Due to their ease of production, dialkyl carbonates, particularlydimethyl carbonate (DMC), are distinguished as starting materials bybeing more readily available. For example, DMC can be obtained by directsynthesis from MeOH and CO (e.g. EP-A 0 534 454, DE-A 19 510 909).

[0008] Numerous publications (e.g. U.S. Pat. No. 2,210,817, U.S. Pat.No. 2,787,632, EP-A 364 052) relate to the reaction of dialkylcarbonates with aliphatic diols:

[0009] In the prior art, aliphatic diols are placed in a vessel togetherwith a catalyst and the dialkyl carbonate (e.g. diethyl carbonate,dibutyl carbonate, diallyl carbonate), and the resulting alcohol (e.g.ethanol, butanol, allyl alcohol) is distilled off from the reactionvessel via a column. In the column, the higher boiling, dialkylcarbonate is separated from the lower boiling alcohol and is recycled tothe reaction mixture.

[0010] Despite its ready availability, the use of dimethyl carbonate(DMC) for the production of aliphatic oligocarbonate diols has onlyrecently become known (e.g. U.S. Pat. No. 5,171,830, EP-A 798 327, EP-A0 798 328, DE-A 198 29 593).

[0011] EP-A 0 798 328 describes the reaction of the corresponding diolcomponent with DMC with distillation of the azeotrope under normalpressure. Uncapping is subsequently effected by vacuum distillation,wherein degrees of utilization of the terminal OH groups of about 98%are achieved under very drastic vacuum conditions (1 torr, about 1.3mbar) (EP-A 0 798 328: Table 1).

[0012] EP-A 0 798 327 describes a corresponding two-step process inwhich a diol is first reacted with an excess of DMC, with distillationof the azeotrope under normal pressure, to form an oligocarbonate, theterminal OH groups of which are present as methoxycarbonyl terminalgroups and are completely inaccessible. After removing the catalyst anddistillation of the excess DMC under vacuum (65 torr, 86 mbar) theoligocarbonate diol is obtained in a second step by the addition offurther amounts of the diol and of a solvent (e.g. toluene) as anentraining agent for the methanol formed. The remainder of the solventthen has to be distilled off under vacuum (50 torr, 67 mbar). Thedisadvantages of this process are the cost of conducting it by the useof a solvent, and the repeated distillation which is required, as wellas the very high consumption of DMC.

[0013] DE-A 198 29 593 teaches the reaction of a diol with DMC, with themethanol formed being distilled off under normal pressure. Apart from asingle mention of the word “azeotrope” in the table headed “Processdiagram of the process according to the invention”, no consideration isgiven there to the overall problem of the azeotrope. It can becalculated from the examples that DMC is used in excess and isazeotropically distilled off. About 27.8% by weight of the DMC used islost.

[0014] According to U.S. Pat. No. 5,171,830, a diol is first heated withDMC and volatile constituents are then (azeotropically) distilled off.After vacuum distillation under drastic conditions (1 torr, 1.3 mbar),take-up of the product in chloroform, precipitation of the product withmethanol and drying the product, an oligocarbonate diol is obtained in ayield of 55% by weight theoretical (loc. cit., Example 6). The degree ofutilization of the terminal OH groups and the azeotrope problems are notconsidered in detail. Although U.S. Pat. No. 5,171,830 mentions, incolumn 5, lines 24 to 26, that the process can be conducted undervacuum, at normal pressure and at elevated pressures, and therefore canbe conducted under all pressures, the particular preferences regardingthe conditions of pressure employed cannot be identified. It is only aprocedure which employs reduced pressure for the removal of volatileconstituents which is mentioned.

[0015] Therefore, in the above publications, which were known hitherto,there is no description of a process, which is simple to carry outindustrially, for the reaction of DMC with aliphatic diols to formoligocarbonate diols with high space-time yields and with high degreesof utilization of the terminal OH groups.

[0016] It is an object of the present invention to provide a simple,productive process, which can also be carried out on a large industrialscale, and which enables oligocarbonate diols to be produced by thetransesterification of aliphatic diols with dimethyl carbonate,optionally with the use of an amount of catalyst which is low enough forthe latter to remain in the product after completion of the reaction,with good space-time yields and with a high degree of uncapping of theterminal OH groups, in simple apparatuses.

[0017] It has now been found that the production of aliphaticoligocarbonate diols by the reaction of aliphatic diols with dimethylcarbonate, with the reaction optionally being accelerated by catalysts,at elevated pressure, results in a high space-time yield. In order tocomplete the reaction and in order to uncap the terminal OH groups(render the latter utilizable), the final residues of methanol andtraces of dimethyl carbonate are removed from the product under reducedpressure, optionally with the introduction of inert gas.

SUMMARY OF THE INVENTION

[0018] The invention relates to a process for producing an aliphaticoligocarbonate diol comprising a) reacting an aliphatic diol withdimethyl carbonate at an elevated pressure, and b) subsequently removingunreacted methanol and dimethyl carbonate under a reduced pressure touncap the terminal OH groups.

[0019] The present invention also relates to a process of making apolymeric material comprising reacting the oligocarbonate diol.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The process according to the invention is conducted underelevated pressure, preferably under a pressure of 1.5 to 100 bar andmore preferably under a pressure of 3 to 16 bar and—depending on thepressure employed—at temperatures from 100 to 300° C., preferably attemperatures from 160 to 240° C.

[0021] At a constant catalyst concentration, an elevated pressureresults in a better conversion of DMC and in a shortening of thereaction times, which has a positive effect on the space-time yield.

[0022] Completion of the reaction and uncapping of the terminal OHgroups (rendering the latter utilizable) are achieved by removing thefinal residues of methanol and traces of dimethyl carbonate underreduced pressure. In one preferred embodiment, completion the reactionand uncapping of the terminal OH groups (rendering the latterutilizable) are effected by introducing an inert gas (e.g. N₂) into theoligocarbonate diol under what is only a slight vacuum of about 150mbar. The gas bubbles are saturated with methanol or DMC and themethanol is thus almost completely expelled from the reaction batch. Bystripping with an inert gas to remove methanol, the equilibrium can befurther displaced in favour of the product, the transesterification iscompleted and the terminal groups are thus rendered utilizable. Thequality of the resulting oligocarbonate diol can be raised to the levelof f DPC-based oligocarbonate diols, and the degree of uncapping of theterminal OH groups increases to more than 98%, preferably to 99.0 to99.95%, most preferably to 99.5 to 99.9%.

[0023] Gas bubbles can be produced by introducing inert gases such asnitrogen, noble gases such as argon, or methane, ethane, propane,butane, dimethyl ether, dry natural gas or dry hydrogen into thereactor, wherein part of the gas stream which leaves the oligocarbonateand which contains methanol and dimethyl carbonate can be rerouted tothe reaction of the oligocarbonate for completion of the reaction.Nitrogen is preferably used. Air can be used if products of low standardwith respect to color are to be made.

[0024] Gas bubbles can also be produced by introducing inert, lowboiling liquids such as pentane, cyclopentane, hexane, cyclohexane,petroleum ether, diethyl ether or methyl tert-butyl ether, etc., whereinthese substances can be introduced in liquid or gaseous form, and partof the gas stream which leaves the oligocarbonate and which containsmethanol and dimethyl carbonate can be recycled to the oligocarbonatefor saturation.

[0025] The substances for producing gas bubbles can be introduced intothe oligocarbonate via simple immersion tubes, preferably by means ofannular nozzles or gasification agitators. The degree of utilization ofthe terminal OH groups which is achieved depends on the duration ofuncapping, and on the amount, size and distribution of the gas bubbles:with increasing duration of uncapping and better distribution (e.g.better distribution and a larger phase boundary, due to a larger numberof smaller gas bubbles when the latter are introduced via a gasificationagitator) the degree of utilization is better. When introducingnitrogen, for example (e.g. at 150 mbar, 8 kettle volumina/hour), usinga gasification agitator, a degree of utilization of about 99% isachieved after one hour, and a degree of utilization of about 99.8% isachieved after about 5 to 10 hours.

[0026] Uncapping, optionally assisted by the introduction of inert gasbubbles into the reaction mixture, is conducted at temperatures from160° C. to 250° C., preferably at temperatures from 200° C. to 240° C.,and under pressures from 1 to 1000 mbar, preferably under pressures from30 to 400 mbar, most preferably under pressures from 70 to 200 mbar.

[0027] During the production of oligocarbonate diols, DMC is distilledoff during the production process. The amount of DMC which has beenremoved by distillation from the reaction batch is determined bydetermining the DMC content of the distillate. This missing amount hasto be made up before stripping off the methanol with inert gases undervacuum to make the terminal groups utilizable. A mixture of DMC andmethanol forms again. The DMC which is lost by the stripping can beadded again, and another part is distilled off again. With each additionthe amount of DMC which is distilled off becomes less, and the desiredstoichiometry is thereby approached.

[0028] This costly procedure can be simplified by combining theindividual addition steps. The amounts of DMC which were distilled offcan be measured in previous batches made with individual addition steps.It is therefore possible subsequently to add the complete amount of DMCtogether in a single step.

[0029] Thus the total amount of DMC required, namely the sum of theamount which is predetermined by the stoichiometry of the desiredproduct together with the amount of DMC which is distilled off whilstthe reaction is conducted, is added directly in the first step.

[0030] During the distillation of the methanol and the uncapping of theOH terminal groups at the end of the reaction when inert gas bubbles areintroduced, a small amount of DMC is lost. This amount has to be takeninto account beforehand by the addition of DMC. The requisite amount canbe determined from previous batches, based on experience.

[0031] In one preferred process variant, an excess of DMC is added atthe start of the reaction which is calculated so that after distillingoff the azeotrope and after uncapping, a product is formed whichcomprises the complete functionality of the terminal OH groups, butwhich has a degree of polymerisation which is too high. A correction isthen made by adding a further amount of the diol component and byconducting a brief transesterification step again. The correction amountcan firstly be determined via the mass balance—by determining the amountof DMC in all the distillates and making a comparison with the totalamount added—or from a measurable property (e.g. OH number, viscosity,average molecular weight, etc.) of the product, the degree ofpolymerisation of which is too high. Renewed uncapping is not necessaryafter this correction, since all the terminal OH groups are alreadyfreely available before the correction, and the addition of the diolcomponents does not result in renewed capping.

[0032] Correction by the addition of DMC, after uncapping bygasification with an inert gas for a product which contains too littleDMC, results in renewed capping.

[0033] According to the invention, the diols and optionally thecatalysts which are present, are placed in a reaction vessel, thereactor is heated, the pressure is applied and DMC is subsequentlymetered in.

[0034] In one embodiment of the invention the process according to theinvention therefore comprises the following steps:

[0035] Placing the diol components and optionally the catalyst in avessel.

[0036] Heating and application of pressure.

[0037] Introduction and reaction of the DMC. The amount of DMC iscalculated so that after removal by distillation in all steps (additionof DMC and uncapping) it is just the requisite amount of DMC oralternatively a slight excess thereof which remains in the reactionsolution. Metered addition can be conducted according to two differentstrategies:

[0038] a) The complete amount of DMC is metered in rapidly in one step.As a consequence, the STY is optimised. A DMC-methanol mixture isdistilled off which has a relatively high DMC content (e.g. theazeotrope), which is considerably less than that obtained in apressureless procedure.

[0039] b) The DMC is metered in in two partial steps. The DMC is firstmetered in slowly, so that DMC-methanol mixtures with low DMC contentsare distilled off. Not until a later point in time, when the DMC contentin the distillate significantly increases, even at the same slow rate ofaddition, is the DMC rapidly metered in, so that a distillate with ahigh DMC content (e.g. a DMC-methanol azeotrope) is formed.

[0040] Procedure b) results in better utilization of the DMC and in aninferior STY.

[0041] Uncapping: rendering the terminal OH groups utilizable byextracting the final residues of methanol and DMC under reducedpressure, optionally by the production of gas bubbles (e.g. by theintroduction of inert gases such as N₂).

[0042] Correction: correction of the stoichiometry, if necessary, byadding further amounts of the diol components and another brieftransesterification.

[0043] It is also possible, of course, for the process according to theinvention to be conducted with an excess of diol. In a procedure of thistype, a correction subsequently has to be made wit DMC. This thenresults in a repeated uncapping step.

[0044] In a further embodiment of the invention up to 100%, preferablyup to 70%, more preferably up to 50% and most preferably up to 30% ofthe DMC is placed in the reaction vessel at the start, together with thediols and the catalyst which is optionally present. The reactor issubsequently closed, heated and pressure is applied. All the distillateis first recirculated to the reactor. The DMC content can be determinedby taking a sample from the distillate stream. Depending on theoptimisation target (DMC yield or STY), a reflux ratio of 100% can beemployed until a minimal DMC content in the distillate is achieved, or adefined time is fixed at which a changeover is made to distillation (aDMC/methanol mixture is distilled off). The residual DMC is subsequentlymetered in, uncapped, and any necessary correction to the stoichiometryis made by adding further amounts of the diol components and by arenewed, brief transesterification.

[0045] Suitable aliphatic diols preferably have 3 to 20 C atoms in theirchain. Examples include 1,7-heptanediol, 1,8-octanediol, 1,6-hexanediol,1,5-pentanediol, 1,4-butanediol, 1,3-butanediol, 1,3-propanediol,2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methylpentanediol,2,2,4-trimethyl-1,6-hexanediol, 3,3,5-trimethyl-1,6-hexanediol,2,3,5-trimethyl-1,6-hexanediol, cyclohexane-dimethanol, and others, aswell as mixtures of different diols.

[0046] Addition products of diols with lactones (ester diols) can alsobe used, such as caprolactone, valerolactone etc., as can mixtures ofdiols with lactones, wherein it is not necessary initially totransesterify a lactone and diols.

[0047] Moreover, addition products of diols with dicarboxylic acids canalso be used, such as: adipic acid, glutaric acid, succinic acid,malonic acid, etc., or esters of dicarboxylic acids and also mixtures ofdiols with dicarboxylic acids or with esters of dicarboxylic acids,wherein it is not necessary initially to transesterify a dicarboxylicacid and diols.

[0048] Polyether polyols can also be used, such as polyethylene glycol,polypropylene glycol and polybutylene glycol, as can polyether polyolswhich are obtained by the copolymerisation of ethylene oxide andpropylene oxide for example, or polytetramethylene glycol which isobtained by the ring-opening polymerisation of tetrahydrofuran (THF).

[0049] Mixtures of different diols, lactones and dicarboxylic acids canbe used.

[0050] 1,6-hexanediol, 1,5-pentanediol and/or mixtures of 1,6-hexanedioland caprolactone are preferably used in the process according to theinvention.

[0051] ε-caprolactone esters are preferably formed in situ, withoutprior reaction, from the raw materials during the production ofoligocarbonate diol.

[0052] In principle, all soluble catalysts which are known fortransesterification reactions can optionally be used as catalysts(homogeneous catalysis), and heterogeneous transesterification catalystscan also be used. The process according to the invention is preferablyconducted in the presence of a catalyst.

[0053] Hydroxides, oxides, metal alcoholates, carbonates andorganometallic compounds of metals of main groups I, II, III and IV ofthe periodic table of the elements, of subgroups III and IV, andelements from the rare earth group, particularly compounds of Ti, Zr,Pb, Sn and Sb, are particularly suitable for the process according tothe invention.

[0054] Suitable examples include: LiOH, Li₂CO₃, K₂CO₃, KOH, NaOH, KOMe,NaOMe, MeOMgOAc, CaO, BaO, KOt-Bu, TiCl₄, titanium tetraalcoholates orterephthalates, zirconium tetraalcoholates, tin octoate, dibutyltindilaurate, dibutyltin, bistributyltin oxide, tin oxalate, lead stearate,antimony trioxide, zirconium tetraisopropylate, etc.

[0055] Aromatic nitrogen heterocycles can also be used in the processaccording to the invention, as can tertiary amines corresponding toR₁R₂R₃N, where R₁₋₃ independently represents a C₁-C₃₀ hydroxyalkyl, aC₄-C₁₀ aryl or a C₁-C₃₀ alkyl, particularly trimethylamine,triethylamine, tributylamine, N,N-dimethylcyclohexylamine,N,N-dimethyl-ethanolamine, 1,8-diaza-bicyclo-(5.4.0)undec-7-ene,1,4-diazabicyclo-(2.2.2)octane, 1,2-bis(N,N-dimethyl-amino)-ethane,1,3-bis(N-dimethyl-amino)propane and pyridine.

[0056] Alcoholates and hydroxides of sodium and potassium (NaOH, KOH,KOMe, NaOMe), alcoholates of titanium, tin or zirconium (e.g. Ti(OPr)₄),as well as organotin compounds are preferably used, wherein titanium,tin and zirconium tetraalcoholates are preferably used with diols whichcontain ester functions or with mixtures of diols with lactones.

[0057] In the process according to the invention, the homogeneouscatalyst is used in concentrations (expressed as percent by weight ofmetal with respect to the aliphatic diol used) of up to 1000 ppm (0.1%),preferably between 1 ppm and 500 ppm (0.05%), most preferably between 5ppm and 100 ppm (0.01%). After the reaction is complete, the catalystcan be left in the product, or can be separated, neutralized or masked.The catalyst is preferably left in the product.

[0058] The molecular weight of the oligocarbonate diols produced by theprocess according to the invention can be adjusted via the molar ratioof diol to DMC, wherein the molar ratio of diol/DMC can range between1.01 and 2.0, preferably between 1.02 and 1.8, and most preferablybetween 1.05 and 1.6. The aforementioned ratio, of course, describes thestoichiometry of the product, i.e., the effective ratio of diol to DMCafter distilling off the DMC-methanol mixtures. The amounts of DMC whichare used in each case are correspondingly larger due to the azeotropicdistillation of the DMC. The calculated number-average molecular weightsof the oligocarbonate diols produced by the process according to theinvention then range, e.g. when 1,6-hexanediol is used as the diolcomponent, between 260 and 15,000 g/mol, preferably between 300 and 7300g/mol, most preferably between 350 and 3000 g/mol. If a diol of higheror lower molecular weight is used, the molecular weights of theoligocarbonate diols produced according to the invention arecorrespondingly higher or lower.

[0059] The process according to the invention makes it possible toproduce oligocarbonate diols of formula HO—R₁—[—O—CO—O—R₁—]_(n)—OH whichhave carbon numbers from 7 to 1300, preferably from 9 to 600, mostpreferably from 11 to 300, in which R₁ is the symbol for aliphatic diolswith 3 to 50 carbon atoms, preferably 4 to 40, and more preferably from4 to 20 carbon atoms.

[0060] The diols can additionally contain ester, ether, amide and/ornitrile functions. Diols or diols with ester functions are preferred,such as those which are obtained by the use of caprolactone and1,6-hexanediol. If two or more diol components are used (e.g. mixturesof different diols or mixtures of diols with lactones), two adjacent R₁groups in a molecule can definitely be different from each other (randomdistribution).

[0061] The process according to the invention enables high qualityoligocarbonate diols to be produced from DMC with good space-time yieldsand with a low degree of capping of their terminal OH groups.

[0062] The oligocarbonate diols which are produced by the processaccording to the invention can be used, for example, for the productionof plastics polymers, fibres, coatings, lacquers and adhesives, e.g. byreaction with isocyanates, or for the production of epoxides, (cyclic)esters, acids or acid anhydrides. They can be used as binder vehicles,binder vehicle constituents and/or as reactive thinners in polyurethanecoatings. They are suitable as components of moisture-hardeningcoatings, or as binder vehicles or binder vehicle constituents insolvent-containing or aqueous polyurethane coatings. They can also beused as building blocks for the synthesis of polyurethane prepolymerswhich contain free NCO groups, or in polyurethane dispersions.

[0063] The oligocarbonate diols which are produced by the processaccording to the invention can also be used for the production ofsynthetic thermoplastic materials such as aliphatic and/or aromaticpolycarbonates, thermoplastic polyurethanes, etc.

[0064] The invention is further illustrated but is not intended to belimited by the following examples in which all parts and percentages areby weight unless otherwise specified.

EXAMPLES

[0065] Examples 1-6 according to the invention are examples of somesynthesis of oligocarbonate diols with an OH number of 53-58 mg KOH/gand a residual methanol content of <10 ppm, produced by a pressurizedprocedure. The comparison example demonstrates a synthesis using apressureless procedure.

Example 1

[0066] 2316 kg 1,6-hexanediol, 2237 kg ε-caprolactone and 0.54 kgtitanium tetraisopropylate were placed in a reaction vessel fitted witha cross-arm agitator. The pressure was increased to 5.2 bar (abs.) withnitrogen. The batch was subsequently heated to 205° C. over 3 hours. Thepressure was held constant at 5.2 bar by means of a pressure controlsystem. After the desired temperature was reached, 800 kg dimethylcarbonate were added over 4 hours via an immersion tube (about 200kg/hour). At the same time, a distillate with a DMC content of about 11%was distilled off into a receiver. Thereafter, the temperature wasreduced to 195° C., and a further 1200 kg dimethyl carbonate weremetered in over 12 hours (about 100 kg/hour). After the metered additionof 400 kg of the 1200 kg, the DMC content in the distillate was about15%, after the metered addition of 800 kg it was about 24%, and at theend of the metered addition it was about 29%. After 4 hours of furtherreaction, the temperature was increased to 200° C. and the pressure wasreduced over 7 hours from 5.2 bar to 100 mbar. 10 Nm³ nitrogen wereintroduced via an immersed inlet tube. The residual methanol wasremoved. After 4 hours, the OH number was 42.5 mg KOH/g and theviscosity was 25,464 mPa.s. A further 80 kg 1,6-hexanediol were added.After a further 9 hours, the OH number was 50.0 mg KOH/g and theviscosity was 20,748 mPa.s. A further 50 kg 1,6-hexanediol were added.After a further 5 hours, the OH number was 57.9 mg KOH/g and theviscosity was 14,513 mPa.s. The residual methanol content was <10 ppm.The total run time was about 48 hours.

Example 2

[0067] 2316 kg 1,6-hexanediol, 2237 kg ε-caprolactone, 0.54 kg titaniumtetraisopropylate and 1000 g dimethyl carbonate were placed in areaction vessel fitted with a cross-arm agitator. The pressure wasincreased to 5.2 bar (abs.) with nitrogen. The batch was subsequentlyheated to 180° C. over 2 hours. The pressure was held constant at 5.2bar by means of a pressure control system. A slight reflux occurred, theliquid from which was returned to the vessel. 1 hour after reaching 180°C., the dimethyl carbonate content in the reflux was about 17%, anddecreased to about 12.5% after a further 5 hours.

[0068] The apparatus was changed over to effect distillation into areceiver and the batch was heated to 194° C. Methanol with a DMC contentof about 12% distilled over. After about 4 hours, the distillation wascomplete.

[0069] 1000 kg dimethyl carbonate were added at a rate of 250 kg/hourvia an immersion tube, and a methanol/DMC azeotrope with a DMC contentof about 20-25% was distilled off. The batch was subsequently heated to200° C. over 1 hour. After stirring for a further 2 hours, the pressurewas reduced to 200 mbar over 7 hours. 8 Nm³ nitrogen were thenintroduced via an immersed inlet tube and the residual methanol wasremoved. After 6 hours, the OH number was 43.2 mg KOH/g and theviscosity was 23,371 mPa.s. 74 kg 1,6-hexanediol were then added. Aftera further 6 hours, the OH number was 48.8 mg KOH/g and the viscosity was20,001 mPa.s. The residual methanol content was 20 ppm. A further 55 kg1,6-hexanediol were added. After a further reaction time of 6 hours, theOH number was 56.5 mg KOH/g and the viscosity was 15,500 mPa.s. Theresidual methanol content was <10 ppm. The total run time was about 45hours.

Example 3

[0070] A 200 liter stirred vessel with a paddle mixer was fitted with apacked column of length 2.5 m (o.d. 11 cm, filled with Pall packings), acondenser and a 100 liter receiver. The distillate caught in thereceiver could be recycled to the reactor via a bottom pump and basalflange.

[0071] 62,353 kg adipol, 60,226 kg ε-caprolactone, 12 g titaniumtetraisopropylate and 23.5 kg DMC were placed in the reactor. Afterrendering the reactor atmosphere inert by evacuating it twice to 300mbar and subsequently filling it with nitrogen, the batch was heated to80° C. over 1 hour and homogenized. A pressure of 5.2 bar was set byfilling with nitrogen under pressure, and the pressure was held constantby means of a pressure control system. The batch was subsequently heatedto 194° C. over 2 hours, and the temperature was held constant for 2hours.

[0072] A further 33.49 kg DMC were metered into the stirred vessel over2 hours at 194° C. After adding the DMC, the batch was heated to 196° C.over 30 minutes and this temperature was held for 5 hours. The batch wassubsequently heated to 200° C. over 30 minutes and the entireDMC/methanol mixture (31 kg, with a DMC content of 25.7%) was distilledoff over 2 hours. The pressure was then reduced to 100 mbar over 1 hourand nitrogen was passed through the batch. After vacuum distillation for7 hours at 100 mbar and 200° C. whilst passing nitrogen through thebatch, an OH number of 60.3 mg KOH/g and a viscosity of 8,667 mPa.s (23°C.) were obtained, after a further 2 hours the OH number was 55.8 andthe viscosity was 13,099 mPa.s, and after a further 7 hours the OHnumber was 53.7 and the viscosity was 15,794 mPa.s.

[0073] The run time was 40 hours and the DMC content in the distillatewas 25.7%.

Example 4

[0074] 9,267 kg 1,6-hexanediol and 0.13 g tetraisopropyl titanate wereplaced in a 20 liter pressure autoclave fitted with a cross-armagitator, a column and a downstream condenser and receiver. Afterrendering the reactor atmosphere inert by evacuating it twice to 300mbar and subsequently filling it with N₂, the pressure in the reactorand the peripheral parts thereof (column, condenser, receiver) was setto 5.2 bar with N₂. The batch was subsequently heated to 197° C. and9.63 kg DMC was metered into the reactor over 6 hours. After the meteredaddition phase, the batch was heated to 200° C. and was distilled for 2hours at this temperature. 6.17 kg of a distillate with a DMC content of25.1% were obtained. The pressure was reduced to 100 mbar and nitrogenwas passed through the batch. After 9 hours, an OH number of 159 mgKOH/g was obtained. The pressure was set to 5.2 bar again and 1 kg DMCwere metered in over 1 hour. After the metered addition, the batch wasfirst stirred for 2 hours, and the pressure was then reduced to 100 mbaragain and the batch was distilled whilst passing nitrogen through it.After a further vacuum distillation for 18 hours at 100 mbar and 200°C., the OH number was 65.5 mg KOH/g. The pressure was increased to 5.2bar, 96 g DMC were metered in, and the batch was stirred for 2 hours,depressurized, evacuated to 100 mbar and distilled whilst passingnitrogen through it. After 19 hours, a product was finally obtainedwhich had an OH number of 56.0 mg KOH/g and a viscosity of 1,699 mPa.s(75° C.).

Example 5

[0075] Reactor: a 20 liter Hagemann reactor fifted with a cross-armagitator, a column and a downstream condenser and receiver. Dimethylcarbonate was metered directly into the reactor via a diaphragm pump(not immersed).

[0076] 6.68 kg 1,6-hexanediol (0.057 kmol), 6.45 kg ε-caprolactone(0.057 kmol) and 1 g tetraisopropyl titanate were placed in the reactor.After rendering the reactor atmosphere inert by evacuating it twice to300 mbar and subsequently filling it with nitrogen, the batch was firstheated to 80° C. over 1 hour and was then heated to 194° C. over 1 hour.

[0077] At 194° C., 6.14 kg dimethyl carbonate (0.068 kmol) were meteredin over about 5 hours. After the metered addition was complete, thebatch was held for 4 hours at 196° C. and the temperature was thenincreased to 200° C. After 2 hours at 200° C. the reactor wasdepressurized to normal pressure and the distillate which had passedover (2.9 kg) was removed from the receiver. After removing thedistillate, the pressure was reduced to 100 mbar and nitrogen was passedthrough the batch. After 6 hours, a viscosity of 42,135 mPa.s and an OHnumber of 29.8 mg KOH/g were obtained. In order to achieve the desiredOH number of 53-58 mg KOH/g, 0.413 kg 1,6-hexanediol were subsequentlyadded, and the batch was held for a further 6 hours at 200° C. and at apressure of 100 mbar whilst passing nitrogen through it. An OH number of45.8 mg KOH/g and a viscosity 21,725 mPa.s were obtained. A further0.150 kg adipol was added. After a further 8 hours, a viscosity of18,330 mPa.s and an OH number of 56.8 mg KOH/g were obtained.

[0078] The total reaction time was about 36 hours.

Example 6

[0079] 9270 kg 1,6-hexanediol, 8950 kg ε-caprolactone were placed at100° C. in a reaction vessel fitted with a cross-arm agitator and acondenser. 1.5 kg titanium tetraisopropylate were added. The pressurewas increased to 5.2 bar (abs.) with nitrogen. The batch wassubsequently heated to 200° C. After the desired temperature wasreached, 7300 kg dimethyl carbonate were equally added over 15 hours. Atthe same time the methanol formed was distilled off as a distillate witha DMC content of about 15-19% by weight. Thereafter, the temperature wasreduced to 180° C., and the pressure was reduced over 3 hours to ambientpressure. The pressure is further reduced over 12 hours to 60 mbar. 2Nm³/h nitrogen were introduced via an immersed inlet tube to take outresidual methanol. The vacuum was further reduced to 20 mbar. After afurther 24 hours at 180° C., the residual non-OH-endgroups (especiallymethylcarbonate groups) were less than 5 mol %. The reactor was cooledto 100° C., brought to ambient pressure and the product filtered. Ityielded 20000 kg of a clear, colorless noncrystralline resin with an OHnumber of 56 mg KOH/g and a viscosity of 15,000 mPa.s at 23° C.

Comparison Example

[0080] Production of the product from Example 5 by a pressurelessprocedure

[0081] Reactor: A 20 liter Hagemann reactor fitted with across-armagitator, a column and a downstream condenser and receiver. Dimethylcarbonate was metered directly into the reactor via a diaphragm pump(not immersed).

[0082] 6.68 kg 1,6-hexanediol (0.057 kmol), 6.45 kg ε-caprolactone(0.057 kmol) and 1 g tetraisopropyl titanate were placed in the reactor.After rendering the reactor atmosphere inert by evacuating it twice to300 mbar and subsequently filling it with N₂, the batch was first heatedto 8020 C. over 1 hour and was then heated to 140° C. over a further 1hour. At 140° C., 6.14 kg dimethyl carbonate (0.068 kmol) were meteredin so that the column top temperature did not exceed 67° C. The time ofmetered addition was about 24 hours at a column bottom temperature of140 to 182° C. After the metered addition was complete, the temperaturewas increased to 200° C. over about 1 hour. 4 hours after reaching 200°C., an OH number of 85.7 mg KOH/g was determined. The batch was cooledto 140° C. and was corrected with 0.357 kg of pure dimethyl carbonatewhilst limiting the column top temperature to 65° C. The time of meteredaddition was about 3.5 hours. The batch was subsequently heated to 200°C. again over 2 hours. Thereafter, it was stirred for 3 hours at 200° C.under normal pressure and for 5 hours at 100 mbar. An OH number of 31.3mg KOH/g and a viscosity of 33,320 mPa.s were obtained thereafter. Inorder to achieve the desired OH number, 0.395 kg adipol was subsequentlyadded. After the reaction had again proceeded for about 3 hours at 200°C. at normal pressure, and for 7 hours at 100 mbar, the OH number was52.5 mg KOH/g and the viscosity was 15,737 mPa.s.

[0083] The total reaction time was about 36 hours.

[0084] Compared with Example 5, the reaction time here was longer, thecatalyst requirement was higher, and there was a greater loss of DMC.

[0085] Although the invention has been described in detail in theforegoing for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be limited by the claims.

What is claimed is:
 1. A process for producing an aliphaticoligocarbonate diol comprising a) reacting an aliphatic diol withdimethyl carbonate (DMC) at an elevated pressure in a reaction mixture,and b) subsequently removing unreacted methanol and dimethyl carbonateunder a reduced pressure to uncap the terminal OH groups.
 2. The processof claim 1 further comprising adding a catalyst.
 3. The process of claim1 further comprising c) adding of inert gas.
 4. The process of claim 1further comprising adding the DMC to the diols in a reaction vesselafter the reactor is heated and the pressure is applied.
 5. The processof claim 4 comprising adding DMC slowly at first into the reactor, andlater increasing the rate of addition to such an extent that aDMC/methanol azeotrope is distilled off.
 6. The process of claim 1comprising adding DMC rapidly in one step.
 7. A process according toclaim 1 comprising adding up to 100% of the theoretical amount of DMC tothe diol, heating the reactor, applying the pressure, refluxing all thedistillate to the reactor until a defined or constant DMC content isobtained in the distillate, distilling off the DMC/methanol mixture andadding the DMC that is lacking compared to the theoretical value.
 8. Theprocess of claim 1 wherein the elevated pressure is between 1.5 and 100bar and the temperature is between 100 to 300° C.
 9. The process ofclaim 8 wherein step b) is performed at a temperature from 160° C. to250° C. and at a pressure from 1 to 1000 mbar.
 10. The process of claim3 comprising introducing the inert gas as bubbles into the reactionmixture.
 11. The process of claim 3 wherein the inert gas is selectedfrom the group consisting of nitrogen, noble gases, methane, ethane,propane, butane, dimethyl ethers, dry natural gas and dry hydrogen. 12.The process of claim 3 wherein the inert gas is prepared from alow-boiling liquid selected from the group consisting of pentane,cyclopentane, hexane, cyclohexane, petroleum ether, diethyl ether andmethyl tert-butyl ether.
 13. The process of claim 1 comprising removingunreacted methanol and dimethyl carbonate in a gas stream and partiallyrecycling the gas stream to the oligocarbonate.
 14. The process of claim1 where the total amount of DMC is the sum of the theoretical amount ofDMC to be reacted with the aliphatic diol plus the amount of DMCdistilled off during the planned reaction time.
 15. The process of claim1 further comprising c) modification of the molecular weight of thealiphatic oligocarbonate by adding more diol components followed byanother transesterification reaction.
 16. The process of claim 1 whereinthe aliphatic diol comprises 3 to 20 C atoms.
 17. The process of claim 1wherein the aliphatic diol comprises an aliphatic ester diol.
 18. Theprocess of claim 17 wherein the aliphatic ester diol comprises anaddition product of a diol with a lactone.
 19. The process of claim 18wherein the lactone is caprolactone or valerolactone.
 20. The process ofclaim 17 wherein the aliphatic ester diol comprises a condensationproduct of a diol with a dicarboxylic acid. 21 The process of claim 20wherein the dicarboxylic acid is adipic acid, glutaric acid, succinicacid, or malonic acid.
 22. The process of claim 1 wherein the aliphaticdiol comprises a polyether polyol.
 23. The process of claim 1 whereinthe aliphatic diol is polyethylene glycol, polypropylene glycol orpolybutylene glycol.
 24. The process of claim 1 wherein the aliphaticdiol is 1,6-hexanediol, 1,5-pentanediol and/or mixtures of1,6-hexanediol and caprolactone.
 25. The process of claim 17 wherein thealiphatic ester diol is formed in situ during the production of thealiphatic oligocarbonate diol.
 26. The process of claim 1, wherein themolar ratio of diol to DMC in the reaction mixture ranges between 1.01and 2.0.
 27. The process of claim 2 wherein the catalyst is a solubletransesterification catalysts.
 28. The process of claim 27 wherein thesoluble transesterification catalyst is used in concentrations up to1000 ppm.
 29. The process of claim 2 wherein the catalyst is anunsoluble transesterification catalysts.